This all started when I put duals in. Putting the driveshaft into phase didn't change anything. Next up to try is to drop the crossmember to the lower position so that my cases are not contacting the body.
I'll have to check this.
How is your driveshaft marked? My High Angle driveshafts have red arrows to make easy to know which way they go.
If the transfer cases are contacting the body I would expect vibration. If it's light contact the weight of a passenger just might be enough to damp it. I suspect you'll resolve the issue by lowering the crossmember.
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1989 4Runner: Dual Ultimate (Inchworm front & Marlin 4.70 rear), Marlin Twin Stick, 1200-lb clutch, 4.88 R&P, Aussie Front, Detroit rear, 30-spline Longs, Long hub gears, ARP hub and knuckle studs & 35x12.50 Cooper STT PRO tires. Marlin rear bumper & sliders. FROR front bumper. SAS with Alcan springs & Rancho 9000XL shocks. Budbuilt Bolt-on traction bar. Custom Interior Cage by Those Guys Rod and Customs.
Moab Tested & Rubicon Approved